Axiology (from Greek ἀξίᾱ, axiā, "value, worth"; and -λόγος, -logos) is the philosophical study of value. It is either the collective term for ethics and aesthetics—philosophical fields that depend crucially on notions of value—or the foundation for these fields, and thus similar to value theory and meta-ethics. The term was first used in the early 20th century by Paul Lapie, in 1902, and Eduard von Hartmann, in 1908.
Axiology studies mainly two kinds of values: ethics and aesthetics. Ethics investigates the concepts of "right" and "good" in individual and social conduct. Aesthetics studies the concepts of "beauty" and "harmony." Formal axiology, the attempt to lay out principles regarding value with mathematical rigor, is exemplified by Robert S. Hartman's Science of Value.